Image forming apparatus

Abstract

An image forming apparatus includes a rotatable image carrying member, a rotatable transfer member cooperative with the image carrying member, and a fixing unit having a fixing nip for nipping and feeding the recording material discharged from the transfer nip while fixing the toner image. In addition, a bowing amount measuring unit measures a bowing amount of the recording material, a storing portion stores a target bowing amount, and a speed controller controls a feeding speed of the recording material. The storing portion stores a plurality of target bowing amounts, which are selectable depending on kinds of the recording material, and the speed controller controls the feeding speed in the fixing nip, and then controls the feeding speed so that the bowing amount is substantially zero at the time when a trailing edge of the recording material leaves the transfer nip.

What is claimed is: 
     
       1. An image forming apparatus comprising:
 a rotatable image carrying member for carrying a toner image; 
 a rotatable transfer member cooperative with said image carrying member to form a transfer nip for nipping and feeding a recording material while transferring the toner image onto the recording material; 
 a fixing unit having a fixing nip for nipping and feeding the recording material discharged from the transfer nip while fixing the toner image transferred onto the recording material; 
 a bowing amount measuring unit for measuring a bowing amount of the recording material which is fed while being nipped by the transfer nip and the fixing nip; 
 a storing portion storing a target bowing amount; and 
 a speed controller for controlling a feeding speed of the recording material by the fixing nip, 
 wherein said storing portion stores a plurality of target bowing amounts, which are selectable depending on kinds of the recording material, and 
 wherein said speed controller is capable of controlling the feeding speed in the fixing nip so that a result of the measurement of the bowing amount measuring unit indicates the target bowing amount, thereafter changing the target bowing amount, and then controls the feeding speed in the fixing nip so that the bowing amount is substantially zero at the time when a trailing edge of the recording material leaves the transfer nip. 
 
     
     
       2. An apparatus according to  claim 1 , wherein said apparatus is operable in a borderless printing mode in which the toner image is formed on an area corresponding to an outside of the recording material and is transferred onto the recording material to an edge of the recording material, and wherein said speed controller effects the control. 
     
     
       3. An apparatus according to  claim 1 , wherein said bowing amount measuring unit is of a non-contact type. 
     
     
       4. An apparatus according to  claim 1 , wherein said image carrying member is a rotatable photosensitive member. 
     
     
       5. An apparatus according to  claim 1 , wherein said image carrying member includes a rotatable intermediary transfer belt, wherein the toner image is transferred from said image carrying member onto said intermediary transfer belt, and then transferred from said intermediary transfer belt onto the recording material. 
     
     
       6. An apparatus according to  claim 4 , wherein said apparatus comprises a plurality of such photosensitive members, and toner images are transferred onto the recording material which is being fed by a feeding belt. 
     
     
       7. An apparatus according to  claim 1 , wherein said bowing amount measuring unit includes a light emitting portion for emitting light toward the recording material, and a light receiving portion for receiving the light reflected by the recording material, and measures a distance between said bowing amount measuring unit and the recording material on the basis of a detection result of said light receiving portion. 
     
     
       8. An apparatus according to  claim 7 , wherein said bowing amount measuring unit is disposed at a position closer to the fixing nip than to the transfer nip in the recording material feeding direction. 
     
     
       9. An apparatus according to  claim 1 , wherein when a borderless printing mode operation is carried out, the feeding speed of the recording material at the time when a trailing edge of the recording material leaves the transfer nip is substantially the same as a moving speed of said image bearing member. 
     
     
       10. An image forming apparatus comprising
 a rotatable image carrying member for carrying a toner image; 
 a rotatable transfer member cooperative with said image carrying member to form a transfer nip for nipping and feeding a recording material while transferring the toner image onto the recording material; 
 a fixing unit having a fixing nip for nipping and feeding the recording material discharged from the transfer nip while fixing the toner image transferred onto the recording material; 
 a measuring unit, provided at a position facing the recording material bridging between the transfer nip and the fixing nip, for measuring a distance between said measuring unit and the recording material; and 
 a speed controller for controlling a feeding speed of the recording material by the fixing nip, 
 wherein said speed controller starts acceleration of the feeding speed in the fixing nip so that the distance measured by said measuring unit approaches a predetermined target value before the time at which a trailing edge of the recording material leaves the transfer nip. 
 
     
     
       11. An apparatus according to  claim 10 , wherein said speed controller is capable of controlling the feeding speed in the fixing nip so that bowing of the recording material between the transfer nip and the fixing nip is eliminated at the time when the trailing edge of the recording material leaves the transfer nip. 
     
     
       12. An apparatus according to  claim 10 , wherein said apparatus is operable in a borderless printing mode in which the toner image is formed on an area corresponding to an outside of the recording material and is transferred onto the recording material to an edge of the recording material, and wherein said speed controller effects the control. 
     
     
       13. An apparatus according to  claim 10 , wherein said image carrying member is a rotatable photosensitive member. 
     
     
       14. An apparatus according to  claim 10 , wherein said image carrying member includes a rotatable intermediary transfer belt, wherein the toner image is transferred from said photosensitive member image carrying member onto said intermediary transfer belt, and then transferred from said intermediary transfer belt onto the recording material. 
     
     
       15. An apparatus according to  claim 13 , wherein said apparatus comprises a plurality of such photosensitive members, and toner images are transferred onto the recording material which is being fed by a feeding belt. 
     
     
       16. An apparatus according to  claim 10 , wherein said bowing amount measuring unit includes a light emitting portion for emitting light toward the recording material, and a light receiving portion for receiving the light reflected by the recording material, and measures a distance between said bowing amount measuring unit and the recording material on the basis of a detection result of said light receiving portion. 
     
     
       17. An apparatus according to  claim 10 , wherein said bowing amount measuring unit is disposed at a position closer to the fixing nip than to the transfer nip in the recording material feeding direction. 
     
     
       18. An apparatus according to  claim 10 , wherein when a borderless printing mode operation is carried out, the feeding speed of the recording material at the time when a trailing edge of the recording material leaving the transfer nip is substantially the same as a moving speed of said image bearing member.